The present invention relates to a burnishing drill providing both drilling and reaming functions.
There are known various types of burnishing drills including drilling edges and reaming edges, that are adapted to form a hole in a workpiece made of a material such as cast iron. The workpiece is first drilled by the drilling edges which are made of hard metal. The drilled hole is further worked by the reaming edges which have an external diameter that is slightly larger than that of the drilling edges, to provide a relatively smooth inner wall of the finished hole.
Since such burnishing drills generally have the linear reaming edges which extend radially outward from a foremost end of the drill and incline axially in a rearward direction, much burden is often applied to the reaming edges while cutting and this results in the lowering of the centering and stabilizing properties of the drill. Therefore, when the rotational center of the reaming edges deflects, the reaming edges can not finish the inner surface smoothly. Especially when the burnishing drills cut a relatively hard workpiece at relatively high feeding and rotating speeds, they tend to provide a finished hole with rough inner face.